1. Field
This Application relates generally to the field of solar energy, and more particularly to increasing energy output of solar energy systems.
2. Relevant Background
Renewable energy sources are increasingly seen as the solution to meeting growing energy demands while reducing greenhouse gas emissions and dependence on fossil fuels. Government energy policies, advances in renewable energy technology, and increased investment have contributed to rapid growth of many different renewable energy technologies.
Solar energy devices are one of the fastest growing segments of the renewable energy landscape. For example, grid-connected photovoltaic (“PV”) solar devices increased at an average annual rate of 60 percent between 2004 and 2009. In 2009 alone, an estimated 7 GW of grid-tied PV capacity was added globally. Other solar energy technologies that are in use or development include concentrating solar power (“CSP”), solar hot water heating systems, solar food cookers, solar crop dryers, solar distilleries and desalinators, and the like.
Cost is a major driver for renewable energy installations. Specifically, renewable energy is typically more expensive per watt than fossil fuel energy including coal and natural gas. The primary costs associated with renewable energy sources such as solar energy are initial capital costs and maintenance costs. While the cost of some solar energy technologies such as photovoltaics are declining due to advances in technology and increases in manufacturing scale and sophistication, solar energy has generally not achieved cost parity with fossil fuel energy sources.
In solar energy systems, efficiency is an important aspect of useful energy output of the system. For example, commercial PV cells typically have less than 20% conversion efficiency of incident solar energy. Other factors affecting solar energy generation include the amount of incident solar energy at the installation site and incident angle of solar radiation on the solar energy system.
To increase efficiency, it is known to orient a solar energy device in the direction of maximum exposure to the sun's energy throughout the day. This orientation control, known as solar tracking, can increase the energy output throughout a day by approximately 20-40% over a fixed orientation solar energy device. Solar trackers generally track the sun's movement in either a single axis or using two axes. Single axis trackers have one axis of rotation, which may be oriented horizontally, vertically, or tilted at some angle to horizontal, with the tilt angle commonly adjusted based on latitude of the installation. Dual axis trackers are able to follow the sun in both horizontal and vertical directions and therefore provide optimum solar energy output for a solar energy system. However, tracking the sun's movement based on a single axis provides the most benefit over a fixed orientation with approximately 30% in increased output, with the additional axis of tracking providing only another approximately 6% in energy output.
Solar tracking is generally accomplished with either an active or passive control system. Active solar trackers use sensors or pre-determined data to find the current position of the sun, and actively orient the solar device to face the sun (e.g., using motors, gears, and computers). While active trackers can use a known solar position to orient and therefore are not prone to inaccuracy due to fluctuations in solar energy (e.g., passing clouds, etc.), they are generally expensive with regard to both initial installation and in maintenance costs.
Passive solar trackers orient a solar energy device without the use of motors. One commercial passive solar tracker uses the sun's energy to move a volatile liquid from a canister on one side of a solar panel to a canister on the other side of the solar panel, which then allows gravity to orient the panel. This technology is expensive, inaccurate, prone to upset by wind gusts, and requires large fluid canisters for orienting large solar energy systems. In addition, this type of system ends the day facing West, and does not re-orient overnight to face East. Accordingly, fluid canister solar trackers take time after the sun comes up in the morning to re-orient themselves to face East. Currently, both active and passive solar trackers can be a substantial cost component in a solar energy system. For these reasons, many solar installations are fixed orientation and do not use solar trackers.